1. Field of the Invention
The present invention relates to a tubular pin tumbler lock unit, and more particularly to a tubular lock that cannot be opened without a precisely corresponding tubular key.
2. Description of the Related Art
A conventional tubular pin tumbler lock unit comprises a tubular lock and a tubular key corresponding to the lock.
The tubular key has a handle and a barrel connected to the handle. Multiple cutouts are respectively defined in a lower periphery of the barrel and a lug extends out of a sidewall of the barrel.
The tubular lock has a cylinder, an upper pin seat, a lower pin seat, multiple upper pins, multiple lower pins, springs connected to a lower end of each lower pin, and a shaft extending out of a center of the lower pin seat. An annular keyway is defined axially in the upper pin seat and a slot is defined radially through the keyway.
The lower pin seat and the upper pin seat are respectively inserted into the cylinder and the keyway is exposed through a circular opening in an upper end of the cylinder. The lower pin seat is securely mounted in the cylinder and the upper pin seat is rotatably mounted on top of the lower pin seat. The upper pins are respectively received in the upper pin seat while upper portions of the lower pins are respectively received into the upper pin seat and lower portions of the lower pins are respectively received into the lower pin seat. An upper end of the shaft is connected to the upper pin seat thereby being rotatable by the upper pin seat.
When the key is not inserted into the keyway, the lower pins extend partially into the upper pin seat so that the upper pin seat cannot be rotated relative to the lower pin seat. When the key is inserted into the keyway, the cutouts are pressed against respective upper pins and push the pins downward so that the lower pins are substantially received into the lower pin seat. Interfacing surfaces between the lower pins and the upper pins align with interfacing surfaces between the lower pin seat and the upper pin seat. Hence, when the key is rotated, the upper pin seat and the connected shaft can rotate relative to the lower pin seat. Thereby a latch bolt connected to the shaft can be pivoted to lock or unlock.
However, a barrel-like object, which is similar to the key, can be inserted into the keyway to rotate the upper pin seat with force such that the conventional key unit can be easily unlocked.
Therefore, the invention provides a tubular lock unit to mitigate or obviate the aforementioned problems.